1. Field of the Invention
The instant invention pertains generally to tools for packing off the annulus between a well casing and a string of pipe received therein and more particularly to such tools which are adapted to be used at the surface of the well.
2. Setting of the Invention
In the usual well cementing operation, casing is lowered into the well bore and thereafter cement is pumped into the casing, through the bottom, and upwardly into the annulus between the casing and the bore. Thereafter pumping pressure is released and the cement is permitted to set.
Sometimes, usually when cementing large diameter casing, a string of drill pipe or tubing is run to the bottom of the casing and cement is pumped through the inner string and into the annulus between the casing and the well bore at the bottom of the well. When using especially large casing and/or when placing a surface string of casing at an extreme depth, it may be necessary to pack off the annulus between the inner string and the casing at the upper end thereof during cementing. This prevents the inward collapse of the casing in response to cement under pressure being pumped into the annulus between the casing and the well bore. Such a pack off also helps to overcome hydraulic forces acting to lift the drill pipe out of position and permits testing the casing for leaks prior to placing cement slurry.
The present invention provides a surface packer and method for using the same in connection with inner string cementing operations. The method and apparatus of the instant invention can be used for other operations such as low to moderate pressure squeeze cementing work behind the surface casing and for spotting and squeezing lost circulation fluids to combat lost circulation zones encountered before a blowout preventer is installed on the wellhead. More generally, the method and apparatus of the invention may be used to seal the upper end of a string of casing whenever required, e.g., for controlling well pressures prior to installation of a blowout preventer.
The apparatus of the instant invention includes an annular body having a lower end adapted for sealing connection to the upper end of a well casing. A packer of the type which may be fluidically set is mounted on the radially inner surface of the annular body and a slip bowl is mounted on the body over the packer. In using the instant invention, the body is mounted on the upper end of a string of casing and a string of pipe is lowered therein through the body. Thereafter, cementing or other operations may be performed while the annulus between the pipe and the casing is maintained under pressure. In one aspect of the invention, the packer is of the inflatable type for permitting inner string manipulation while maintaining the seal between the inner string and the casing. In another aspect of the invention, the body is adapted for quick connection to the upper end of the casing string.